A droplet actuator may include one or more substrates configured to form a surface or gap for conducting droplet operations. The one or more substrates establish a droplet operations surface or gap for conducting droplet operations and may also include electrodes arrange to conduct the droplet operations. The droplet operations substrate or the gap between the substrates may be coated or filled with a filler fluid that is immiscible with the liquid that forms the droplets.
Droplet actuators are used in a variety of applications, including molecular diagnostic assays, such as enzymatic assays and immunoassays. In one application, enzymatic assays and immunoassays are used as part of a routine testing process to test newborn infants for various genetic disorders. For example, enzymatic assays may be used to test for various lysosomal storage diseases (LSD), galactosemia and biotinidase deficiency (BIOT). Immunoassays may be used to test for congenital hypothyroidism (CH), congenital adrenal hyperplasia (CAH) and cystic fibrosis (CF). Current enzymatic assay and immunoassay technologies used in newborn testing are based on 96-well microtiter plate compatible systems. Specimens are punched automatically from a neonatal dried blood spot (DBS) sample into several plates (i.e., one punch for each test to be performed) and each plate is manipulated according to a specific assay protocol. Each assay may require a separate laboratory section with a manager, one or more technologists, and equipment dedicated to the assay. Overall, the system is labor intensive (although one or more steps are at least partially automated) and reagent and equipment costs can be high. Because the current system is labor intensive and costly, testing is generally restricted to centralized laboratories and often unavailable in developing countries. Therefore, there is a need for new approaches to newborn testing.